PCI: Unexport pci_save_aer_state()

pci_save_aer_state() and pci_restore_aer_state() are only used in
drivers/pci, so don't expose them to the rest of the kernel.  No functional
change intended.

Link: https://lore.kernel.org/r/20230609222500.1267795-2-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>